The present invention relates to a stilbene derivative having high compatibility with a binder resin, high sensitivity and excellent stability, a method of producing the same, and an electrophotosensitive material containing the stilbene derivative used in image forming apparatuses such as electrostatic copying machine, facsimile and laser beam printer.
In the image forming apparatuses, various organic photosensitive materials having the sensitivity within a wavelength range of a light source used in the apparatus are used. Recently, the organic photosensitive material has widely been used because it is easily produced as compared with a conventional inorganic photosensitive material and that it has advantages such as wide range of choice of photosensitive materials such as electric charge transferring material, electric charge generating material and binder resin, and high functional design freedom.
The organic photosensitive material includes a single-layer type photosensitive material wherein an electric charge transferring material and an electric charge generating material are dispersed in the same photosensitive layer, and a multi-layer type photosensitive material comprising an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material, which are mutually laminated.
Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho Sho) No. 50-31773 and Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho Hei) No. 7-244389 disclose a stilbene derivative as the electric charge transferring material used in the organic photosensitive material.
However, the stilbene derivative disclosed in the above patent applications is not uniformly dispersed in the photosensitive layer and charge transfer hardly occurs because of its poor compatibility with a binder resin. Therefore, the stilbene derivative itself has high charge mobility. However, when using the stilbene derivative as the electric charge transferring material in the photosensitive material, its characteristics can not be sufficiently exhibited so that the residual potential of the photosensitive material increases and the sensitivity to light becomes insufficient.
An object of the present invention is to solve the technical problems described above and to provide a novel stilbene derivative suited for use as an electric charge transferring material of an electrophotosensitive material, and a method of producing the same.
Another object of the present invention is to provide an electrophotosensitive material having improved sensitivity and repeatability as compared with a conventional electrophotosensitive material.
To attain the objects described above, the present inventors has studied intensively and found the following fact. Among the stilbene derivative, a compound, wherein molecular structures of triphenylamino groups located at both sides of a benzene ring in a molecular center are unsymmetric with respect to the benzene ring, is superior in compatibility with a binder resin to a conventional stilbene derivative and has a large charge mobility. Thus, the present invention has been completed.
That is, the present invention is directed to a stilbene derivative, a method of preparing the same, and an electrophotosensitive material using the same.
1. A stilbene derivative wherein molecular structures of triphenylamino groups located at both sides of a benzene ring in a molecular center are unsymmetric with respect to the benzene ring.
2. The stilbene derivative according to the term 1, which is represented by the general formula (1): 
wherein R1 to R24 are the same or different and each represents an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted aryl group, an optionally substituted aralkyl group, a hydrogen atom, or a nitro group; R25 and R26 each represents a vinylene group; at least one of the pairs of a combination of Rn and Rn+5 and a combination of Rm+Rm+2 represent different substituents; at least two substituents of the group consisting of R1 to R5, R6 to R10 R11 to R15, and R16 to R20 represent a hydrogen atom; n represents an integer of 1 to 10; and m represents 21 or 22.
3. The stilbene derivative according to the term 2, wherein at least one of the pairs of R21 and R23, R22 and R24, and R25 and R26 represent different substitution positions from that of a nitrogen atom attached through a benzene ring.
4. The stilbene derivative according to the term 2, wherein at least one of R1, R6, R11 and R16 represent an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted aryl group, and an optionally substituted aralkyl group.
5. The stilbene derivative according to the term 1, which is represented by the general formula (2): 
wherein R1 to R24 are the same or different and each represents an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted aryl group, an optionally substituted aralkyl group, a hydrogen atom, or a nitro group; R25 and R26 each represents a vinylene group; Rn and Rn+5 each represents the same group; Rm and Rm+2 each represents the same group; at least one of the pairs of R21 and R23, R22 and R24, and R25 and R26 represent different substitution positions from that of a nitrogen atom attached through a benzene ring; n represents an integer of 1 to 10; and m represents 21 or 22.
6. The stilbene derivative according to the term 5, wherein at least one of R1, R6, R11 and R16 is an optionally substituted alkyl group, an optionally substituted alkoxy group, an optionally substituted aryl group, or an optionally substituted aralkyl group.
7. A method of producing the stilbene derivative of the term 2, which comprises reacting an aldehyde derivative represented by the general formula (3): 
wherein R1 to R5, R11 to R15, R21, R22 and R25 are as defined in the general formula (1), with a triphenylamine phosphate derivative represented by the general formula (4): 
wherein R6 to R10, R16 to R20, R23 and R24 are as defined in the general formula (1).
8. A method of producing the stilbene derivative of the term 2, which comprises reacting a formylated triphenylamine derivative represented by the general formula (5): 
wherein R1 to R5, R11 to R15, R21 and R22 are as defined in the general formula (1), with a monostilbene derivative represented by the general formula (6): 
wherein R6 to R10, R16 to R20, R23, R24 and R26 are as defined in the general formula (1).
9. A method of producing the stilbene derivative of the term 5, which comprises reacting an aldehyde derivative represented by the general formula (3): 
wherein R1 to R5, R11 to R15, R21, R22 and R25 are as defined in the general formula (1), with a triphenylamine phosphate derivative represented by the general formula (4): 
wherein R6 to R10, R16 to R20, R23 and R24 are as defined in the general formula (1).
10. A method of producing the stilbene derivative of the term 5, which comprises reacting a formylated triphenlamine derivative represented by the general formula (5): 
wherein R1 to R5, R11 to R15, R21 and R22 are as defined in the general formula (1), with a monostilbene derivative represented by the general formula (6): 
wherein R6 to R10, R16 to R20, R23, R24 and R26 are as defined in the general formula (1).
11. An electrophotosensitive material comprising a conductive substrate and a photosensitive layer formed on the substrate, the photosensitive layer containing at least one of the stilbene derivatives of the term 1.
12. An electrophotosensitive material comprising a conductive substrate and a photosensitive layer formed on the substrate, the photosensitive layer containing at least one of the stilbene derivatives of the term 2.
13. An electrophotosensitive material comprising a conductive substrate and a photosensitive layer formed on the substrate, the photosensitive layer containing at least one of the stilbene derivatives of the term 3.
14. The electrophotosensitive material according to the term 11, wherein the photosensitive layer is a single-layer type photosensitive layer containing an electric charge generating material.
15. The electrophotosensitive material according to the term 12, wherein the photosensitive layer is a single-layer type photosensitive layer containing an electric charge generating material.
16. The electrophotosensitive material according to the term 13, wherein the photosensitive layer is a single-layer type photosensitive layer containing an electric charge generating material.
17. The electrophotosensitive material according to the term 14, wherein the electric charge generating material is one or more member selected from the group consisting of a metal-free phthalocyanine, a metal phthalocyanine, a perylene pigment and a bisazo pigment.
18. The electrophotosensitive material according to the term 15, wherein the electric charge generating material is one or more member selected from the group consisting of a metal-free phthalocyanine, a metal phthalocyanine, a perylene pigment and a bisazo pigment.
19. The electrophotosensitive material according to the term 16, wherein the electric charge generating material is one or more member selected from the group consisting of a metal-free phthalocyanine, a metal phthalocyanine, a perylene pigment and a bisazo pigment.
In the present invention, the stilbene derivative represented by the general formula (1) or (2) is a particularly preferable compound when using in the photosensitive layer of the electrophotosensitive material because of its excellent compatibility with a binder resin and large charge mobility.
The stilbene derivative represented by the general formula (1) or (2) is a novel compound which is not disclosed in Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho Sho) No. 50-31773 and Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho Hei) No. 7-244389, and is characterized in that molecular structures of triphenylamino groups located at both sides of a benzene ring in a molecular center are unsymmetric with respect to the benzene ring. In addition, the compound has a higher compatibility with a binder resin than that of the compounds disclosed specifically in the above patent applications, and has a high charge mobility.
Therefore, an electrophotosensitive material having high sensitivity and improved repeatability can be obtained by using the stilbene derivative (1) or (2) as the electric charge (hole) transferring material in the electrophotosensitive material. The stilbene derivative, wherein at least one of R1, R6, R11 and R16 is an optionally substituted alkyl, an optionally substituted alkoxy group, an optionally substituted aryl group, or optionally substituted an aralkyl group, has good compatibility with a binder resin because of its poor symmetry of the molecule, and it is particularly preferred.
The stilbene derivatives (1) and (2) can be obtained by the production method described in the term 7 (hereinafter referred to as a production method (A)) or the production method described in the term 8 (hereinafter referred to as a production method (B)).
The electrophotosensitive material of the present invention is an electrophotosensitive material comprising a conductive substrate and a photosensitive layer formed on the substrate, the photosensitive layer containing at least one of the stilbene derivatives represented by the general formulas (1) and (2).
As described above, since the stilbene derivative represented by the general formula (1) or (2) is contained in the photosensitive layer, the electrophotosensitive material of the present invention is superior in sensitivity to light on charging and exposure because of its high speed of transferring electric charges (holes) generated in the electric charge generating material, that is, large charge mobility. As a result, according to the electrophotosensitive material of the present invention, the sensitivity is higher than that in case where a conventional stilbene derivative is used as a hole transferring material, and the repeatability is improved.
The photosensitive layer is preferably a single-layer type photosensitive layer containing at least one of the stilbene derivatives represented by the general formulas (1) and (2), and an electric charge generating material and an electron transferring material.
The electrophotosensitive material of the present invention has a specific operation and effect capable of contributing to attain high speed and high performance of various image forming apparatuses such as electrostatic copying machine and laser printer, because of the above features.